1. Field of the Invention
The invention generally relates to dispensing and more specifically to a dispensing tool that operates in combination with a replaceable, insertable cartridge with a follower that is a part of the cartridge. The tool includes a grip-type actuator that drives a pressure plate against the follower. In a specific embodiment, the invention is a caulking gun that operates a short-body discharge assistant to produce a metered discharge of caulk.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
Sealant, adhesive, mastic, and other extrudable, settable construction materials may be supplied in sealed, typically cylindrical cartridges. The front end of a cartridge is temporarily sealed by a sheet of film or foil behind a leading nozzle. The user can pierce or break the seal immediately before using the contents, thus revealing the fresh and readily extrudable substance for discharge through the nozzle. The rear end of the cartridge is open and houses a follower that rests against the rear of the contents. Therefore, the method of use is to push the follower against the contents, discharging the contents out the nozzle. When the cartridge is empty, which equates to the follower having advanced to the rear of the nozzle, the cartridge is discarded.
A tool or more specifically, a caulking gun is used to apply the contents of such a cartridge as desired. A caulking gun typically provides a drop-in holder or receiver for the cartridge. The receiver supports the cartridge in semi-cylindrical, open-topped body that allows the cartridge to be dropped-in, with a front wall having a passage for the cartridge nozzle to extend beyond the front of the tool. The rear end of the receiver is joined to a discharge assistant that includes a pressure plate for engaging the follower. The pressure plate is sized to fit into the cartridge in order to drive forward the follower. Under user control, a grip-type actuator may operate either intermittently or continuously to drive the pressure plate. Conventionally, a pushing device interconnects the actuator with the pressure plate. Typically, the actuator incrementally advances the pushing device to advance the pressure plate. When the pressure plate has been fully advanced and cartridge has been emptied, the user operates a thumb release mechanism associated with the pushing device that allows him to withdraw the pressure plate from the cartridge and allowing the cartridge to be removed from the receiver.
Many different technologies can be used in a pushing device, including pneumatic, hydraulic, electric, and mechanical. However, in practical terms the pushing device will almost always be mechanical and very simple in structure. Unquestionably the most common pushing device is a pushrod with a bent or hooked rear end that serves as a handle. The associated actuator is a pivoted trigger on the handle of the caulking gun and a bindable advancement plate mounted on the pushrod via an aperture through the plate that is slightly larger than the diameter of the pushrod. The trigger operates by pushing forward on the bindable plate near its edge, thereby pushing forward on only one edge of the plate, which first tilts the plate into a binding position and then pushes forward the entire plate. The tilt causes the aperture of the advancement plate to bind with the pushrod, resulting in the entire pushrod being pushed forward with the advancement plate. In this way, trigger motion is converted into forward motion of the pressure plate. A spring pushes back on the advancement plate from its front face and untilts the advancement plate as soon as the trigger releases, leaving the advancement plate in an untilted position on the pushrod.
A spring-loaded brake plate constantly engages the pushrod in a tilted position to prevent rearward movement, with the result that the pushrod stays in its advanced position regardless of the advancement plate being released to untilted position. However, a thumb release allows the user to press the brake plate to release its grip on the pushrod, which allows the user to retract the pushrod when desired by pulling back on the handle.
A notorious problem with caulking guns of the type described is the substantial length of the pushrod. It is as long as the cartridge plus the actuator, with still additional length protruding from the rear of the actuator. When a new cartridge is in the gun, the pushrod extends to the rear by a maximum length, nearly doubling the length of the gun. A standard or popular size of caulk gun has a pushrod that extends approximately nine inches from the rear of gun. The rear extension is an aggravation to the user because it interferes with usage, especially in confined areas like inside cabinets, in closets, and behind toilets, to name a few.
Several technologies have been used to eliminate or shorten the pushrod of a caulking gun. WO 03/064056 discloses a caulking gun that replaces the pushrod with a pair of pushing chains that are fed from sides of the gun to combine in the center as a rigid pusher. This technology suffers the disadvantage of lacking the accepted open top receiver for inserting new cartridges. Instead, the cartridge is inserted at the front of the receiver and held in the gun by retaining clips. A further disadvantage is that the new cartridge must push back the pressure plate and pushing chains while initially being inserted, which adds difficulty to inserting the cartridge far enough to close the retaining clips.
U.S. Pat. No. 6,926,177 to Scott et al teaches a telescoping plunger that replaces the pushrod. The telescoping mechanism includes a turnbuckle that extends or retracts the pressure plate, and an electric drill is coupled to the gun to spin the turnbuckle. It is evident that hand operation of a turnbuckle is impractical. The necessary addition of the drill adds another dimension of excess size, plus it add considerable weight that tends to fatigue the user.
U.S. Pat. No. 6,640,998 to Kern teaches the use of a fixed pressure plate joined to the trigger assembly. The trigger draws the cartridge backwards against the fixed pressure plate, eliminating the need for a pushrod. Instead, the trigger assembly cuts a slot from the rear of the cartridge so that the cartridge can continue to move backwards against the pressure plate. This technology has the disadvantage of requiring increased force on the trigger to cut the slot, and when the cartridge is empty, it is needlessly complex to pull the trigger assembly free from the slot.
It would be desirable to produce an internal drive for a caulking gun, such that the maximum length of the caulking gun could be reduced in comparison with guns employing a full length pushrod. At the same time, it would be desirable to maintain the familiar features found in standard caulking guns, such as the open-topped receiver, the hand operated trigger and thumb release, and a light weight.
To achieve the foregoing and other objects and in accordance with the purpose of the present invention, as embodied and broadly described herein, the method and apparatus of this invention may comprise the following.